1. Field of the Invention
Forced air duct systems, especially for purposes of heating and air conditioning, employing fan control methods and apparatus. Means for controlling temperature in response to changes in pressure.
2. Description of the Prior Art
Conventional forced air heating or cooling systems, or combined heating and cooling systems, employ one or more air ducts leading to various areas such as rooms or zones in a building. There is usually a main or primary air duct leading from the furnace of air cooling means and the main or primary duct branches out into various areas. Dampers may be employed to balance the system. Temperature sensing thermostats are located in various areas but of course delivery of warmer or cooler air to one area affects the other areas and upsets the balance of the system. Due to the high cost of energy and the anticipated higher cost considerable attention is being given to more efficient operation of forced air heating and cooling systems in an effort to find reasonably comfortably conditions which are as efficient as possible. It has been determined previously that effective fan control is one means of dealing with the problem. For example, in U.S. Pat. No. 3,814,173 the various control functions are provided in response to electrical signals which are digital in nature and the air fan associated with the furnace or cooling coils has its speed changed by digital increments in response to the total demand for heated or cooled air by means of an SCR controller for the fan motor and the SCR controller has a speed setting potentiometer with a plurality of taps enabling different segments of its total resistance to be shorted out, so as to increase accordingly input voltage to the fan motor. This system involves the coordination of multiple thermostats and the resolution thereof for averaging SCR fan speed control. Due to the expense involved and the cost of installing and maintaining SCR fan speed control equipment and the coordination of multiple thermostats there are certain disadvantages in comparison with the present system which does not rely solely upon thermostat or temperature reading but rather employs a means for sensing the internal duct pressure and the use of a standard comparing instrument to increase duct pressure by changing fan speed. In addition, fan speed is varied mechanically through the use of the spring loaded pulley which can be purchased on the open market in conjunction with a drive mechanism for changing the tension on the drive belt between the pulley and the motor. The present system does not require expensive solidstate electronics and can be applied to modify any new or existing forced air system.